1. Technical Field
The present invention relates to a gear pump in which a driving gear and a driven gear that exhibit a pumping action are accommodated in a pump casing and a printing apparatus provided with the same.
2. Related Art
In the related art, a gear pump that transports an ultraviolet-curable ink is known as this type of gear pump (refer to JP-A-2012-21516).
The gear pump is provided with a drive shaft that inputs the power from a motor via a power transmission mechanism, a driving gear attached to the drive shaft, a driven gear that meshes with the driving gear, and a fixed shaft that rotatably supports the driven gear. The gear pump is provided with a case (pump chamber) that has a suction port and a discharge port, and that accommodates the driving gear and the driven gear along with the drive shaft and the fixed shaft.
Meanwhile, a controller that controls the motor alternately executes reverse driving and forward driving of the motor a plurality of times whenever a threshold time elapses after the motor starts forward driving. The driving and driven gears are helical gears and reverse driving and forward driving are alternately performed so that the thrust force alternately works in the forward and reverse directions and the drive shaft and the driven gear move slightly, as appropriate, in the axial direction. In so doing, ink that lubricates between the driving gear and a first bearing portion that supports the driving gear and ink that lubricates between the driven gear and the fixed shaft that supports the driven gear flow. Although the ultraviolet-curable ink undergoes a polymerization reaction and is cured induced by heat or the like, the curing of the ink is suppressed by the flow, and fixing of the drive shaft and driven gear is prevented.
In the gear pump of the related art, a problem arises in that not only does the control of the motor become complicated, but also the transport of the ultraviolet-curable ink that is the original function becomes unstable due to the forward and reverse driving.
The relationship between the drive shaft and the first bearing portion and the relationship between the driven gear and the fixed shaft are included in the relationship between the shaft and the bearing in a relative sense. Therefore, as long as the clearance between the shaft and the bearing is formed with high accuracy, it is thought that friction at those parts is reduced (an ultraviolet-curable ink properly functions as a lubricant (lubricating oil)), excess heat generation is suppressed, and curing of the ultraviolet-curable ink is prevented.
However, in the gear pump of the related art, since a bearing part which supports a driving shaft and a fixing shaft at both ends thereof is formed in a case (pump casing), there is a problem in that it is difficult to form the gear pump with high accuracy. That is, in a pair of bearing parts which supports each shaft, it is necessary to form the bearing parts so that each of axis lines thereof coincides with each other, and in pairs of adjacent bearing parts, it is necessary to form the bearing parts so that the axis lines are parallel with each other. In such cases, in a case (pump casing) which requires a divided structure, it is particularly difficult to form a total of four bearing parts mutually with high accuracy. Therefore, the shaft with respect to the bearing part is easily supported in an inclined manner. Since a rotating shaft is directly contacted with the bearing part, frictional heat is generated.